Method and apparatus for measuring frequency



H. NYQUlST METHOD AND APPARATUS FOR MEASURING FREQUENCY FiledDec. 19, 1923 Dec. 21 1926. 1,611,224

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- INVENTOR 15. M [M195 By 1/? W A TTORNE Y Patented Dec. 21, 1926.

.:- iunrfion renames-ma.uaasua a Application filed D ecenflier 1a, 192;.f'jseria1n 381,596

f A principalobject of my invention is to provide a new and improved method and suitable apparatus for measuring the frequency of analternating current. Another this specification byway of illustration. It

will be understood that the following description refers to these examples and-that the invention defined in the appended f1a m a {Referring to the drawings, Figure 1 is a diagram of one embodiment of my invention, and Fig. 2 is a diagram of another embodiment of my invention. V InFig. l,the electromot'rve force of fre- 2 quency to. be measured v is applied through -,,the. circuit 1 and transformer 3 to the grid of the three-electrode vacuum tube 4. A standard frequency alternating current electromotive. force is also applied in the circuit .2 and the same transformer 3 to the .sameg ridz, I f W r is "well understood, a number of different frequencies will be found in the output-circuit of the tube l. Among these will bea current of frequency equal to the difference of the frequencies in' the circuits 1 and 2. Since these two frequencies are very near :together, this; difference frequency will be very low. The other frequencies in the output will be much higher and will be substantially shunted by the condenser 5 and the difference frequency will be a plied through the transformer 6 to the win mg of the re- ?Accordingly, the armature 8 will vibrate at this low difference frequency. On one contact, the condenser 9-will charge through the resistance 10 from the battery 11. On the other contact, the condenser9 will discharge through the resistance 12 and the measuring instrument 13. Each cycle of movement of the armature 8 will put a definite quantity of electricity from the I PHONE AND'TELEGRAIEH'GOMIPANY ,A CORPORATION F NEWLYORK. 3'

.ment- 13, so that the integralcurrent thro gh the measuring instrument, '13! will be -proportional to the frequencyof vibration of-the armature 8.

nnany nyeursr, or Manson-HEIGHTS,nnw'gironx. time Fro QTEL E .12.

The measuring instrument -13"- mayi be 3 I calibrated-to givevthe difference frequency or it may be calibrated to give the "frequency to be measured in" the circuit 1.- I The'displacement of the indexin the instrument 13 will be proportional to the difference 1 fr'e-v quency and hence will give the "frequency to be measured very accurately. 7

Fig. 2 is the same as Fig. 1 as described above to the vibrating armature- 8.- The circuit as'soc'iated therewith may be looked upon as a Wheatst o'ne bridge. 5 Adjustment is made at 15, so that when the frequency to be measured is normal, that is,""when the frequency difference is normal as compared with the stan dard, then the reading in the measuring, instrument 13 is zero It' will be seen that when the condenser chargesand dischargesat a 'slowerrate than 'norrnah'the bridge will unbalanced one way and there a will be a reading 1n the measuring instrument One way from zero. On the other'hand, when the condenser 9. charges'and discharges'ata faster rate than normal, the bridge will be unbalanced the other way and the instrument 13 will read the other way from zero.. 5 i

The difference frequ'encycomponen't in the output of the vacuum tube 4, to whichrefgerence vhas been made, is due to the'nonl-inear relation between output current and input,

voltagei It is war understood that,"in--"gen-" eral, when the output current is .a nonlinear function of the input voltage, and when two sine waves 0f different: frequency of input voltage are superposed,- then there will "be a variety of components in the output and among them will be a component whose frequency is the difference between the two input frequencies.

Referring to Fig. 1, it will be seen that by means of the two circuits 1 and 2 there are two electromotive forces superposed on the grid of the three-electrode vacuum tube 4. The well known space charge effect'is in existence for the discharge between the filament and the plate, and by means of the grid the electromotive force thereof is superposed on the space charge effect to modify its influence in determining the current in condenser 9 through the measuring instruthe plate circuit.

I claim: i q

1. The method of measuring the .fre

current of non-linear .relation to said combined electromotive forces, separating out from" the said resultant current the component of difference frequency, generating thereby a pulsatory current of this fre-' \ing of a circuit in which an electromotive quency, and measurin 'the integral value thereof to determine t e frequency difference between the iven' electromotive force and the standard ee'ctromotive force.

2. The methd of measuring the frequency of a given alternating electromotive force which consists in superposing an electro: motive force of that jrequ'ency together with an electromotive force of slightly different standardv frequency on the space 7 charge effect in a vacuum tube, establishing a pulsatory' current of frequency determined by the difference frequency component in the output of that tube, and measuring the integral'value of said pulsatory curv rent.

3. The method of measuring the frequency' of an alternating electromotive force which consists in combining it with an electromotive force of slightly different standard frequency, producing a current of nonlinear relation to the combined electromo tive forces as aforesaid and comprising a difference frequency component, applying this difference frequency component to determine the charge and discharge of a condenser at the difference rate, and measuring the condenser current. l

4. A frequency measuring device consisting of a circuit in which an electromotive force of that frequency and an electromotive force of a standard frequency are superposed, and means to measurethe difference between the two frequencies and to indicate it quantitatively.-

superpose a slig tly different standard freuency in 'the same grid circuit whereby t e output current of the tube will com rise a component whose frequency is the difference of the frequencies of the said two input electromotive forc'es, and means operated by said component to measure the difference frequency and indicate it quantitatively.

6. Means to measure a frequency. consistference frequency, a condenser, means to.

[of the said fre uency" is applied, means to charge and discharge said condenser at the rate of the difference frequency, and a measuring instrument, to measure the integral condenser current. q

' 7. The method of easuring the frequency of a given electl d motive force which .consists in combining this electromotive force with an electromotive force of slightly different standard frequency to produce a current whose frequency-is the difference of the two electromotive force frequencies,

and indicating the magnitude of this dif-.

the given electromotive force, an output ircuit associated with said device, means within the device to generate a current in said output circuit of the difference frequency, and means to indicate the frequency of said current.

In testimony whereof, I have signed my name to this specification this 18th day of December, 1923.

HARRY NYQUIST. 

